tmf: Add SwtBot tests for importing as experiment

tmf: Add SwtBot tests for importing as experiment

The following test cases are added:
- create experiment when importing from directory
- create experiment when importing from archive
- create experiment during import with experiment name validation

Utility methods are added to SwtBotUtils to create an experiment and
to clear the experiment folder.

Change-Id: I3fc5f83efc811f267cfc31a48c603915c9d74646
Signed-off-by: Bernd Hufmann <Bernd.Hufmann@ericsson.com>
Reviewed-on: https://git.eclipse.org/r/68083
Reviewed-by: Hudson CI
Reviewed-by: Matthew Khouzam <matthew.khouzam@ericsson.com>
Tested-by: Matthew Khouzam <matthew.khouzam@ericsson.com>